The present invention relates generally to torsional vibration dampers, and more particularly to an automated active damping system for damping resonance torsional vibrations in a member capable of transmitting a torque.
In almost all systems in which torque is transmitted via a rotating shaft, such as an engine, pump, compressor, etc., the shaft is subject to fatigue failure due to the long term presence of torsional vibrations. The same can be said for stationary members of a system that are capable of transmitting a torque, which also makes them subject to the detrimental effects of torsional vibrations. As a result of the mass properties, every member capable of transmitting a torque, whether it be stationary member, a gear or a rotating shaft, has a number of natural torsional frequencies which are capable of excitation. Each natural frequency corresponds to a resonance mode of the member. For example, in a mode one vibration, the ends of a member twist back and forth with respect to each other while a single node location along the length of the shaft remains untwisted. In the case of a rotating shaft, this twisting motion is superimposed on the mean rotational speed of the shaft. In a mode two vibration, two node locations are located along the length of the member that remain untwisted. These node locations can be determined for a given system either empirically or by approximation using available software tools.
In one example application, such as some automotive drivelines, only lower mode resonance torsional vibrations are of concern since they naturally occur in relatively larger amplitudes. Higher modes are usually of lesser concern because they generally occur with relatively small amplitudes that a properly engineered driveline can withstand without significant damage. In some vehicle drivelines, the crank shaft of the vehicle's internal combustion engine has as many as nine resonance modes that are excitable over the operating range of the engine in magnitudes sufficient to induce fatigue stress. Because of the trend to reduce weight in engines, torsional vibrations are becoming more of a concern to automotive engineers. This weight reduction renders the individual components more sensitive to torsional vibrations. In the past, resonance torsional vibrations were effectively ignored by automotive design engineers by utilizing increased component weight due to the relatively large design safety factors that increased component and overall weight. Motor vehicle drivelines are but one of a number of technologies that could benefit from a light weight torsional vibration damping system that is easily incorporated into the given machinery.
Although the lowest resonance mode generally has the largest vibration amplitude relative to the other modes, a resonance vibration in any of the modes can quickly grow sufficiently large in amplitude that the shaft, gear or other member may break or at least have its life shortened due to unnecessary torsional fatigue. New materials, such as new metallic alloys, may have effectively extended the fatigue life of certain high stress components, but material sciences cannot eliminate the long term fatigue problems caused by torsional vibrations. In most cases, resonance vibrations will shorten the life of a torque transmitting member and eventually result in a fatigue failure. In extreme cases, resonance torsional vibrations can grow so quickly in amplitude that the torque transmitting member literally tears itself and any attached machinery apart.
Fatigue failures in gears, rotating shafts and other torque transmitting members are most often attributable to the prolonged presence of one or more resonance mode torsional vibrations. The useful life of much machinery is often dictated by the fatigue life of its most critical torque transmitting member. For instance, in the case of an internal combustion engine, the crank shaft is often the first piece of machinery to break due to cyclical fatigue stress occurring at a node location along the length of the shaft. What is needed is a damping system that actively damps harmful resonance torsional vibrations below a threshold amplitude.